Depth control system for underwater vehicle

ABSTRACT

A depth control system for an underwater vehicle having a pressure transducer for providing a frequency output proportional to depth and having means for comparing the measured depth with a preset depth. The output frequency of the pressure transducer is accurately measured by a high frequency crystal-controlled oscillator and counter and this high frequency count is stored in a binary register and compared with a reference register to determine whether the pressure is greater, less than, or approximately equal to the preset value.

United States Patent [72] Inventor Afl u 3,273,122 9/1966 Chandler I Mercer Island, Wash. 3,351,895 11/1967 Cupp et al. 114/2352 X [21] Appl. No. 831,950 3,469,821 9/1969 Gross et a1. 114/2352 X [22] 1969 Primary Examiner-Malcolm A. Morrison [45] Patented July 20, 197] A t l E J Smith 731 Assignee The United States of America as s i my H H L h d p 8 re med by the s o the Navy ttorneysgar rower, osc e an au pl use CollIgnon [54] DEPTH CONTROL SYSTEM FOR UNDERWATER VEHICLE 2 Claims, 2 Drawing Figs.

U,S- .5. A depth control system for an underwater vehi- [51] Ill!- Cl ..G06l 15/50, l ha in a pressure transducer for providing a, frequency 8 output proportional to depth and having means for comparing [50] Field Of Search 235/1502, the measured depth with a preset depth The output frequency 1513, 340/1461, 3 of the pressure transducer is accurately measured by a high 1 601, 603 frequency crystal-controlled oscillator and counter and this high frequency count is stored in a binary register and com- [56] References pared with a reference register to determine whether the pres- UNITED STATES PATENTS sure is greater, less than, or approximately equal to the preset 3,117,303 1/1964 Byme 340/150X value.

coo: coImAuo (I2 Pifl sec.)

II an a NARY PRESSURE an: coun rzn TRAPSWCER (couurs I559) 1/ /2 /3 STOP srow START Io an BINARY e BIT BINARY :21 :3 coumzn coum'cn 15 14 16 ,7 l,

a err BINARY STORAGE Io BIT BINARY REGISTER STORAGE (M) REGISTER 19 (x) l /a 1. 01:31 L

PARA'l' OR In an D-A T CONVERTER 2/ 2:222:22 V REGISTER 3a IEgiA JlI ND S A LOG PuFIER L 1 DEPTH 22 3/ 3:"

32 ODER perm con'raot. SYSTEM FOR UNDERWATER VEHICLE BACKGROUND OF THE INVENTION The present invention relates to a system for controlling and recording the depth of a self-propelled underwater research vehicle. Any one of various digitally preset operating depths may be utilized during an underwater run. The underwater SUMMARY OF THE INVENTION The present invention utilizes the output frequency of a pressure transducer to generate a measurement period which is accurately measured by a high frequency crystalcontrolled oscillator and counter. The high frequency count is then stored in an l8-bit binary register. The most significant 8 bits are compared with an 8 -bit reference register to determine whether'the pressure is greater, less than, or approximately equal to the preset value. If the two 8-bit registers are the same, the least significant 10 bits of the storage register are allowed to control a digital to analog converter which generates an error voltage proportional to the deviation from the preset depth.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of a preferred embodiment of the present invention; and

FIG. 2 is a graphic illustration of waveforms showing outputs for various depths.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, there is shown a pressure transducer 11 which provides a frequency output which is proportional to depth. By way of example, pressure transducer 11 might be a Vibrotron Pressure Transducer, which is manufactured by United Control of Redmond, Washington. As the Vibrotron Pressure Transducer is sensitive to temperature change, the transducer is preferably housed in a Constant Temperature Heater Chamber which is also manufactured by United Control. In .an embodiment of the present invention which was built and tested at the Applied Physics Laboratory, University of Washington, in Seattle, Washington, pressure transducer 1] had a pressure range from 0 to 4500 p.s.i., with a corresponding frequency output rangefrom 25.2 kHz. to 19.6 kHz.

The output (f,,) from pressure transducer II is gated by gate 12, which receives a start command every l/l2 second, and the output 0",) is accumulated in a l l-bit binary counter 13. The first count of counter 13 opens gate 14 to pass the output of crystal oscillator 15, which has a frequency of 5,898,240 Hz. Counter 13 is designed to accumulate 1569 counts (N,) and then closes gates 12 and 14. As the frequency of pressure transducer 11 varies between 25.2 kHz. at 0 p.s.i. and l9.6 kHz. at 4500 p.s.i., the count (N,) of counter 13 was selected at I569 which makes the sampling period 62 ms forf, =25.2 kHz. and T= 80 ms. forf,,=l9.6 kHz. as:

As the longest period for T will be when f, is the smallest, that is, when f,,=l9.6 kHz., the longest period for T will be 80 ms. thus assuring that counter 13 will complete its count within 1/12 of a second. It can thus be seen that counter 13 will complete its count before a new start command will be received by gate 12. Gate I4 is opened during period T and the output from oscillator 15 will be gated to an 18-bit counter which is shown as a lO- bit binary counter 16 and an 8-bit binary counter 17. The count accumulated in counters l6 and 17 during period T varies between 366,000 for T=62 ms and 472,000 for T =80 ms. As the maximum accumulation for an l8-bit counter is 2" or 262,144, it can be seen that counters '16 and l7 will always fill and recycle once during T. The relationship between the l8-bit count (N f, is as follows: 455 5,898,240 and therefore v N2 I It is convenient to let N be represented as follows: (4) N 1024) (M+256)+X where M is the number accumulated in counter 17 during T, and 256 accounts for the fact that both counters l6 and 17 l8-bit) have recycled once. X represents the remaining count in counter 16 at the end of T. Combining equation (3) and (4) provides:

. counters 16 and 17 can be available for the next sample.

Storage register 18 drives a digital to analog converter 21 (resistive ladder network) thus generating a voltage proportional to X. A differential input operational amplifier 22 is used to invert and shift the output of converter 21 so that a depth control signal is obtained which varies between +3 and 3 volts for X between 0 and 1023.

The count in storage register 19 is compared digitally in comparator 23 with a preset count placed in a depth reference register 24. The count in register 24 represents the depth (in meters) at which the undersea vehicle is to travel and this depth can be changed, as will be hereinafter described. When the count in register 19 is less than the count in register 24, indicating that the measured depth is lessthan the preset depth, the output of the digital to analog converter 21 is clamped to 0 volts by digital comparator 23. This causes the depth control signal to go to +12 volts thereby saturating the vehicles depth control system in the down direction. Similarly, when the count in register 19 is greater than the count in register 24, indicating that the measured depth is greater than the preset depth, the output of the digital to analog converter 21 is clamped to +4 volts by digital comparator 23, causing the depth control signal to go to l2 volts. This causes the vehicles depth control system to be switched to the up direction. When the count in register 19 equals the count in register 24, indicating that the measured depth is close to the preset depth, the digital comparator output is open, allowing the output of converter 21 to vary linearly with X. Because of the DC level shift introduced by amplifier 22, the depth control (error) signal is 0 when X =5 l 2.

Four sets of switches, '31, 32, 33, and 34 are provided for setting different counts into register 24. Switch 31 is permanently wired to provide a count in register 24 which represents 0 pressure and is used as a testing channel. Switches32, 33, and 34 are each sets ofeight binary weighted, single pole, double-throw switches, which are used to select, prior to launch of the underwater vehicle, three different operating depths. It should be understood, of course, that if a greater number of operating depths are desired, it is merely necessary to add additional binary switches. Switches 31, 32, 33 and 34 are connected through gates 35, 36, 37 and 38, respectively, to register 24 and the opening of the desired gate is controlled by a receiver and decoder 39, which receives an acoustic depth command from a surface vessel.

OPERATION Prior to diving, switches 32, 33, and 34 are first set for the desired depth. By way of example, in a recent dive of a Self- Propelled Underwater Research Vehicle (SPURV) operated by the Applied Physics Laboratory, University of Washington, depths of 420 meters, 732 meters, and 1495 meters were f, Depth (meters) Pressure (p,s.i.)

25,1383 43.0 6248 24,8621 2l3.9 1H2.) 24,6583 338.4 494.0 24,4585 459.8 67l.4 |9,972.2 29l6.0 4257.4

Referring now to FIGURE 2 of the drawing, there are shown graphs of the outputs from amplifier 22, comparator 23, and storage register 18. With the operating depth being 102 meters less than the preset depth, the count in register 19 will be less than the count in register 24 and comparator 23 will cause the output of converter 21 to be clamped to 0 volts. This causes the depth control signal (output of amplifier 22) to go to +12 volts, thereby saturating the SPURV depth control system in the down" direction. It can be seen in FIG. 2 of the drawing, that this condition continues until the deviation from the preset depth is -34 meters. At this depth, the count in registers l9 and 24 will be equal and the connection between comparator 23 and converter 21 will be open", and the output from amplifier 22 will vary linearly with the output (X) of storage register 18. The depth control output signal will vary between +3 volts and 3 volts when X varies between 0 and 1023.

When the operating depth deviation becomes greater than 34 meters, the count in register 19 will be greater than the count in register 24 and the output of converter 21 will be clamped to +4 volts thereby generating a l 2 volt depth control signal which will saturate the SPURV depth control system in the up" direction.

I claim:

1. A depth control system for an underwater vehicle comprising:

a pressure transducer providing a frequency output proportional to water depth,

a first gate,

means for periodically opening said first gate,

a first binary counter for registering a fixed number of counts, said binary counter being connected through said first gate to the output of said pressure transducer,

a second gate receiving opening and closing commands from said first binary counter,

first and second storage registers,

a crystal oscillator providing a frequency output, means for connecting said frequency output to said first and second storage registers through said second gate,

a reference storage register for storing a digital count representing a preselected water depth,

comparator means for comparing the count in said first storage register with the count in said reference storage register and providing an output signal when said counts are unequal,

converter means connected to the output of said second storage means for providing an analog output signal proportional to the count stored in said second storage means, and

means connected to the outputs of both said comparator means and said converter means for providing an analog depth control signal for controlling said vehicle.

2. A depth control system for an underwater vehicle as set forth in claim 1 having a plurality of binary switches connected through separate switch gates to said reference storage register and havingfmeans for selectively opening said switch gates whereby ifferent counts representing different preselected water depths can be switched into said reference storage register. 

1. A depth control system for an underwater vehicle comprising: a pressure transducer providing a frequency output proportional to water depth, a first gate, means for periodically opening said first gate, a first binary counter for registering a fixed number of counts, said binary counter being connected through said first gate to the output of said pressure transducer, a second gate receiving opening and closing commands from said first binary counter, first and second storage registers, a crystal oscillator providing a frequency output, Means for connecting said frequency output to said first and second storage registers through said second gate, a reference storage register for storing a digital count representing a preselected water depth, comparator means for comparing the count in said first storage register with the count in said reference storage register and providing an output signal when said counts are unequal, converter means connected to the output of said second storage means for providing an analog output signal proportional to the count stored in said second storage means, and means connected to the outputs of both said comparator means and said converter means for providing an analog depth control signal for controlling said vehicle.
 2. A depth control system for an underwater vehicle as set forth in claim 1 having a plurality of binary switches connected through separate switch gates to said reference storage register and having means for selectively opening said switch gates whereby different counts representing different preselected water depths can be switched into said reference storage register. 